It is common to incorporate seekers into missiles, for guiding the missile onto a target. When a new missile is being developed it must be tested to ensure that the design is robust and that it behaves the way it is expected to. Tests are carried out at all stages of development on the components and sub-systems, but a test is needed for the complete, assembled missile, in order to check that the sub-systems work together as intended, and that the missile is capable of doing the job it is required to do. The missile sub-systems can be tested simultaneously in a representative environment by firing the missile against a test target at a missile firing range. This is an essential part of any new missile development programme, although it is very expensive and time consuming. A way of significantly reducing the number of missile firings required is to use validated representative performance models. Hardware In The Loop (HWIL) testing allows the interaction and response of many of the missile sub-systems to be tested repeatedly in a controlled environment, at much lower cost and with much faster timescales than firing trials, to provide confidence in both the models and the missile sub-systems.
Guided missiles contain a seeker for autonomous target tracking and interception. The seeker contains a detector that responds to electromagnetic radiation, either RF, optical or infrared, that is emitted or scattered by the target. Target radiation detected by the seeker is used to determine target bearing and motion, and thus to determine the necessary guidance commands to direct the missile's motion. If the guidance is correct the missile controller will use the seeker information to steer the missile on a trajectory that will intercept the target. HWIL testing simulates this process in a controlled manner in the following way. The front of the missile containing the seeker, i.e. real hardware, is mounted in a cradle that is able to rotate about all three axes. A representative image of a target at a particular range is then projected to the missile seeker to simulate a real target, by means of a target scene generator. The target scene generator is also mounted so that it can be rotated in azimuth and elevation, relative to the seeker, to simulate target motion.
The missile seeker responds to the simulated movement and bearing of the target image and sends data to a missile controller, which then determines appropriate guidance signals to send to other missile sub-systems, such as the actuators for the fins. The overall aerodynamic and kinetic response of the missile to these guidance signals is then modelled, to determine the angular motion to be imposed on the 3-axis cradle, and the effect on the image of the target due to the modelled aerodynamic kinetic response of the missile. Any required changes to the simulated position and motion of the target image are input to the scene generator, which then projects a modified image to the seeker, and then the cycle is repeated. This arrangement is referred to as closed-loop testing, as the consequences of the signals from the missile controller are fed into the target scene generator, which changes the image seen by the seeker and thus the input to the controller, which affects the target scene again, and so on, without operator intervention. Testing is also performed in real-time. The simulated target image grows larger as time progresses, representing the missile's flight towards the target. If the missile is operating correctly the cyclical process allows the complete target engagement to be tested from launch to the point where the missile fuze would be expected to operate. The sub-systems not normally tested by this process are the fuze, the warhead, and the motors.
The target scene generator is a key component of HWIL testing. However, there are currently limitations on the types of seeker that can be tested in this way. In this regard, HWIL systems for testing missiles with optical or infrared seekers typically only test “passive” seekers i.e. where the seeker passively views the radiation emitted by the scene, and does not provide its own radiation to illuminate or floodlight the scene. By contrast “active” seekers contain their own radiation sources to provide scene illumination, and respond only to the wavelengths of those generated sources. Such active seekers based on laser radar include at least one laser source, and detect only laser wavelengths in a selected narrow-band so that the effect of ambient background noise radiation is reduced. The laser source may be carried by a missile or may be a semi-active laser (SAL). In this latter case, the laser emitter may carried by an aircraft or ground personnel and used to illuminate a target for detection by the sensor of the missile.
Testing of such active ladar seekers in HWIL arrangements is not feasible with typical HWIL test equipment, however, because known target scene generators are not capable of generating an image in the format that an active ladar seeker can recognise.
Testing of SAL seekers in HWIL arrangements is similarly not feasible with typical HWIL test equipment. Even though a SAL sensor is ‘passive’ and does not carry its won laser source, it responds only to pulsed laser radiation, and thus requires a target scene generator that can provide the required laser pulses with the correct timing from the different parts of the SAL's seeker's field of view.
Equipment for HWIL testing of ladar seekers is known to be in development, although such test equipment is typically based on a target scene generated by an array of independent, actively controlled light sources.